This invention relates to the method and apparatus for providing signaling interconnectivity between mobile telephone networks of different regions where the respective regions use disparate telecommunications standards and/or protocols.
Messages necessary for roaming, including authentication, registration, temporary assignment of roaming numbers to support calls to a roamer, and Short Message Service, among others, will utilize services of the described system.
“Signaling System 7” or “SS7” is a set of signaling protocol used by essentially all telephone equipment throughout the world. Around the world, there is general agreement on the lowest-layer protocols (called Message Transfer Part, MTP, and Signaling Connection Part (SCCP), and the higher-layer protocols (ISUP, TCAP and MAP).
However, there are two disparate standards for implementation of network signaling protocols in common use, ANSI and ITU. Outside the United States and Canada, including Europe and Asia, essentially all telephone end nodes and networks and interior nodes (e.g., mobile switching center, class 4 and 5 switches, etc.) use a signaling protocol agreed within the International Telecommunications Union (ITU). ITU protocols use an addressing scheme called “ISDN Numbering Plan (E.164), as well as mobile global title” (MGT) (E.214). Message packets in ITU systems represent caller and called party telephone numbers in a numbering plan format designated either “E.164” or E.214.” In almost all cases, the address in an E.164 representation is the phone number as dialed for an international phone call. For example, an E.164 address of a U.S. telephone would be the country code “1,” then the area code (“212” for New York City, or “416” for Toronto), and the seven-digit local phone number. In contrast, within the U.S. and Canada, network packets use number formats specified by the American National Standards Institute (ANSI). The addressing scheme used in ANSI is called “ISDN Numbering Plan (E.164), and international mobile station identity” (IMSI)(E.212). Called party numbers are represented in ANSI packets in a numbering plan format designated as “E.212” if they are destined to an HLR for certain messages, or E.164 if they are destined for the end subscriber unit, or certain nodes such as an MSC. Calling Party addresses are normally coded in E.164 format.
A hybrid numbering plan address format, designated “E.214” allows certain messages with E.212 format to be routed in ITU networks. In an E.214 address, the layout format for an address is a combination of E.164 and E.212. Essentially, the country and network information is formatted in E.164, while the unique customer identification within the network is formatted as E.212.
In SS7 network protocols, another level of addressing is provided by a “point code,” a number that identifies a node, much as a zip code on a mailing envelope identifies the post office that serves a particular street address. Within North America, ANSI point codes are 24 bits long, allowing the specification of 16 million discrete destinations. The 24-bit ANSI point code generally uses the first 8 bits to identify a network, (Verizon, Cingular, T-Mobile, etc.), the second 8 bits to identify a cluster of nodes within the network and the last 8 bits to identify a node within the cluster. In ITU countries, an ITU point code is only 14 bits long, allowing the specification of 16,536 discrete locations. The 14 bit ITU point code generally uses the first 3 bits to identify a region, the next 8 bits to identify a network, and the last 3 bits to identify a node in that network.
Note that any end-point telephone in the world has a valid address in numbering plan E.164. GSM mobile units are also uniquely identified by an E.212 number. However, an interior node of the ANSI network essentially never has an ITU point code, and vice-versa.
Further details of ANSI and ITU protocols are discussed in section II.A, below.
A mobile telephone handset must use the air interface and protocols of the local base stations in whatever geographic region it is to be used. Thus, some mobile handsets are equipped with circuitry that allows the handset to switch between the different sets of air protocols.
Even where a mobile phone can be switched to use correct local protocol, a local mobile switching center cannot service that phone until the mobile switching center confirms the identity of a mobile subscriber. The mobile switching center can only confirm that identity if it can reach the “home location register” database for that phone. Where the mobile switching center uses one communications protocol and the computer storing the registration database uses another, this confirmation is impossible.